In a second step, similarly to the Kalman smoother [1]} and to the forward-backward algorithm [2]}, we derive two different backward recursions that allow the consideration of future observations without relying on any additional parameters. We also prove by induction that the two are equivalent. In contrast with the work of Garner and Tong [3]}, the unit-wise recurrence is here derived using transition probabilities instead of a context relevance gate.
